ANÁLISIS ESTADÍSTICO

The distal limbs of 17 dairy animals were collected, individually identified and bagged. The age, as determined by ear tag or dentition (Dyce et al., 2002), breed and cause of death, if applicable, was recorded for each individual. The limbs were washed and stored at 3-5 ° C until measurements were made. The majority of measurements (12/17) were made within 96 hours, but for four animals measurements were made within 8-9 days of death. Sources included a local abattoir (1/17); Massey University post mortem room (animals with a cause of death unrelated to lameness) (9/17) and non-lame cull dairy cows euthanased on farm for reasons unrelated to this study (7/17).

Seven measurements were made on both claws of all feet (Figure 2.1a). All measurements were made using a flexible tape measure (to the nearest millimetre, mm), except for toe angle which was measured using an engineer’s angle finder. All measurements were taken twice and the mean of the two values used for modelling.

After measurement of the claw variables, the right front and left hind limbs were then processed for volume estimation using water displacement. The process and the apparatus

used initially were based on the description by Scott et al. (1999); i.e. the volume of water that was displaced when the claws were immersed to the level of the coronary band was collected and recorded (Figure 2.1b). The only difference was that for time efficiency, the claws were not clipped or disarticulated but the limb simply sectioned longitudinally from between the claws with a band saw, so that the medial and lateral claws could be separately assessed for volume. An elastic band was used to restrain bulging fat from the sectioned digital cushion and prevent it entering the water.

However, although Scott et al. (1999) reported an R2 of 0.999 for repeated volume estimates on the same claws using their hydrometer, the process proved difficult to replicate. The key problems encountered were firstly: deciding when the water had equilibrated. Clark et al. (2004), using a similar method to measure claw volume, allowed a five minute equilibration period, whereas Scott et al. (1999) did not report an equilibration time. Secondly siphoning of water into the collection vessel. Consequently this method was abandoned in favour of measuring water displacement by removing the displaced water by suction with a syringe back to a reference line.

Figure 2.1a: Illustration of the seven variables measured on both claws of the hind feet of 17 dairy cows. Modified from Scott et al. (1999) i, abaxial groove; ii end of the axial white line.

A. Toe angle: Angle of dorsal border to weight-bearing surface;

B. Length of dorsal border from skin: horn junction at coronary band to apex of toe;

C. Claw lengthon the palmar/plantar surface from apex of toe to point where ground contact is lost (cm);

D. Distance from the point where the coronary band meets the flexure of the dorsal border to the abaxial groove along the coronary band (proximal);

E. Distance from the apex of the toe to the abaxial groove along the wall horn (distal); F. Length of the abaxial groove from the coronary band to base of claw;

G. Claw widthon the palmar/plantar surface, at widest point of claw in area of sole/bulb junction.

Figure 2.1b: water displacement equipment after Scott et al. (1999). Water displaced by the claw overflows to collection vessel via rubber tubing.

Figure 2.1c: Modified water displacement equipment: Water level was set to a predetermined mark until there was no parallax with the lines marked on either side of the container; a 60mL syringe was used. The claw was immersed to the level of the skin: horn junction at the coronary band and held in place with a retort stand as shown. Water line was returned to preset level by suction and volume measured in the calibrated measuring cylinder shown (cm3_).

A transparent container, with straight sides, just big enough to accept the claws and allow adjustments without the claws contacting the sides, was used (Figure 2.1c). A water level line was marked on both sides of a container so that the two lines could be visualised through the container. At eye level with no parallax, the two lines superimposed into one.

Water level was set to this line using a 60 mL syringe. The clean, dried, claws were individually immersed to the skin: horn junction of the coronary band and held in place with a retort stand. The position of the claw was adjusted, using the retort clamp, until the water line was at the skin: horn junction at the dorsal flexure and at the heel bulb, in a dorso- palmar/plantar plane, and also in an abaxial-axial plane (the axial landmark being the skin/ horn junction in the interdigital region). Water was removed with a 60 mL syringe until the meniscus fell back to the set water level line. The volume removed was recorded in cm3 to the nearest 0.5 cm3 using a calibrated measuring cylinder. The procedure was performed twice (from scratch) for each claw to obtain an average value for modelling. The difference between the measured and predicted values (Scott et al., 1999) was investigated.

Experiment 2: Investigation of the relationship between predicted volume and